Theserials.com was a dangerous website, but the site was taken down in 2009. The site gave out free "serial numbers" to programs like AVG, however, these were fake serial numbers, as these serial numbers are actually trojan droppers.
If the user installs a serial number, the user would then install an application, which would be the virus itself. When the user runs the file, an installer would load up. The program would then open up through CMD.exe, then it would automatically enter serial.exe, which would then add both readme.exe and setup.exe. It would then make the user download another file from the website, if the user clicks and downloads these links, it would drop a trojan virus.